1. Field of the Invention
The present invention relates to a 2/2 directional seat valve with direct control. More particularly the present invention relates to a 2/2 directional seat valve comprising a housing and a seat piston.
2. Discussion of the Prior Art
The concept of directional valves encompasses all valves which are employed to control the starting, stopping and changing of the direction of the volumetric flow of a pressure medium. The designations of directional valves are based on the number of utility connections and the number of controller positions. Thus, a valve with two utility connections and two controller positions is designated a 2/2 directional valve. Based on their design, a distinction is made between directional slide valves, directional seat valves and rotary slide valves. The basic design of a directional seat valve is described in the Hydraulic Trainers' Book, Volume 1, "Principles and Components of Fluid Technology, Hydraulics" ("Grundlagen und Komponenten der Huidtechnik, Hydraulik") (October 1991, p. 203ff). The seat valve typically includes a housing, a seat piston, and a closing spring. The closing spring pushes the seat piston to seat in a seat area within the housing to seal the valve. For high-pressure applications, the seat valves usually include housings and seat pistons made of steel. Thus, for example, a 4/4 directional value consisting of four 2/2 directional seat valves becomes very heavy in terms of weight, which is a great disadvantage for use in aircraft construction.
It has already been suggested that the housing be made of light metal or a light metal alloy and the known seat pistons of steel be arranged therein. Attempts have shown that it is not possible to do this, or only possible with complications, because the pairing of steel and light metal in the area of the seal seating leads to cold taps or the premature wearing out of the seating. In both situations, the area relationships change as a result, so that the force of the closing spring is not sufficient to balance the increasing counter-force. As a result of this, leakages develop. One possible solution is to provide the area of the seating in the light-metal housing with a steel covering. However, this is very expensive to design and manufacture.